I recently purchased a return ticket from them to visit my in-Laws, travelling to Montenegro via Vienna, but when a family emergency required I travel a week early before I flew out direct on another airline, expecting to use the return portion of the Austrian booking.

When I arrived to check in for the return flight, I was advised that the airline had cancelled my ticket as I had not used the outbound portion, and that the only way they would let me fly on their (half-empty) flights was if I purchase danother ticket. So I had no choice but to pay twice (once the expensive last minute price) for the same seats!

I complained to Austrian Airlines staff at Vienna during transit and they claimed it is in their terms & conditions but I could not find it anywhere on their website - and in fact they quote £50 to change the dates booked - but I wanted the same flights I booked originally.

I have emailed Austrian twice and sent a registered letter of complaint but they did not bother to respond.

I don't believe that - it never happened to me before - not even with RyanAir or Easyjet. The terms & conditions are wrapped in legalese but even after the even it is hard to read them as saying "if you don't take the plane out we will cancel your return journey and to hell with you" - Austrian are not very polite and obviously totally incapable of seeing things from the customer's perspective - taking refuge in T&Cs in several pages of small type are not the actions of an ethical supplier.

They finally replied to one of my emails along those lines- several weeks later. Don't travel with Austrian if you have a choice.

This is an utterly unfair practice, but it is indeed very common in the legacy carriers. The reason it doesn't happen with Ryanair and Easyjet is that they don't really sell return tickets..they sell two single tickets, one each way. It is packaged as a return, but the pricing is based on two one way tickets, and if you cancel or no show for one, it will not automatically cancel the other. The reason given why Austrian, Lufthansa, Air France and BA for example do cancel them is that they offer so called dynamic pricing to attract "hub" customers. Let me give you an example\;

BA may charge £500 for a return ticket from London to Hong Kong
AirFrance may also charge £500 for a return ticket from Paris to Hong Kong

In order for BA to win some transfer business from Paris to Hong Kong via London, their price has to be better than £500, because why would you go through the hassle of changing in London if you can go direct for the same price. So BA price the ticket from Paris to Hong Kong at £420.

This all went swimmingly until the internet came along. Suddenly, customer realised they would save significant sums of money by booking a ticket from Paris to Hong Kong via London, throwing away the Paris to London portion of the ticket and boarding in London.

In addition, because single fares are typically purchased by business travellers (and tickets are priced on demand, not on costs) the airlines often had single fares which were higher than returns. The same rules applied. So Austrian might charge £100 return for a flight from Vienna to London to encourage volume. However, the cost of a single from London to Vienna could be £200. To stop people buying the return for £100 and just throwing away the first leg, the airlines introduced a requirement that you must have completed the first leg of the journey to make the second leg valid.

There is no real justification for this ridiculous and byzantine pricing, other than maintaining the airlines right to fleece customers. Sadly, no regulator has ever tried to stop this practice and I think it is something we just have to live with. BA appear to have dropped it for most domestic and European flights and seem to be selling tickets on the same basis as the low costs.. however, it remains for long haul.

There is little you can do... except avoid the legacy carriers for intra-european flights and use low costs.